EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Melting and subsolidus phase relations of Fe-Si-S alloys at Mercury’s core conditions 

Serena Dominijanni1, Simone Anzellini2, Alexander Kurnosov3, Guillaume Morard4, Silvia Boccato1, Timofey Fedotenko5, and Daniele Antonangeli1
Serena Dominijanni et al.
  • 1Institut de Minéralogie de Physique des Matériaux et de Cosmochimie (IMPMC), Sorbonne Université, Muséum National d’Histoire Naturelle, CNRS UMR 7590, 75005 Paris, France
  • 2Diamond House, Harwell Science and Innovation Campus, Fermi Ave, Didcot OX11 0DE, United Kingdom
  • 3Bayerisches Geoinstitut, University of Bayreuth, Bayreuth, Germany
  • 4Institut des Sciences de la Terre, Université Grenoble-Alpes, 1381 rue de la Piscine F- 38610 Gières
  • 5Photon Science, Deutsches Elektronen Synchrotron, Hamburg, Germany

The internal structure of Mercury holds key information regarding the planet’s formation and its peculiar magnetic field. Waiting for incoming observations by BepiColombo, current knowledge of the interior structure of Mercury relies primarily on geodetic and surface chemistry data collected by MESSENGER. Results from spectral and compositional analysis supplemented by cosmochemical evidence indicate that light elements such as S, and Si are most likely alloyed to Fe in Mercury’s core. This notion is further supported by the very reducing redox conditions (from -2.6 to -7.3 log units below Fe-FeO oxygen buffer) predicted to occur during the planet’s differentiation that argue for significant quantities of Si and S partitioned into metallic iron. Thus, it is of primary importance to determine the Fe-Si-S phase diagram and to understand the high pressure and high temperature properties and thermodynamic behavior of Fe-Si-S alloys at conditions directly relevant for Mercury’s core. Very recently the binary Fe-FeSi phase diagram has been established at Mercury’s core conditions, but phase and melting relations in the Fe-Si-S ternary system still are poorly constrained, in particular at the relatively low pressures and temperatures relevant for Mercury’s core.

To address this issue, we performed angular dispersive powder X-ray diffraction experiments in laser-heated diamond anvil cells on selected composition in the Fe-Si-S system (i.e., Fe-4S-6Si, Fe-16S-6Si, Fe-4S-12Si, and Fe-16S-12Si, all in wt. %) at the P02.2 Extreme Conditions beamline at DESY Synchrotron facility (Germany). For all compositions, eutectic melting and subsolidus phase relations were investigated up to about 45 GPa. Ex situ chemical analysis of the recovered run products were performed at the IMPMC laboratory on the extracted FIB thin sections cut throughout the heated spots.

Here we will present preliminary results on the eutectic melting and Fe-Si-S phase relations as a function of pressure, temperature and composition, with specific focus to the conditions expected within the core of Mercury.

How to cite: Dominijanni, S., Anzellini, S., Kurnosov, A., Morard, G., Boccato, S., Fedotenko, T., and Antonangeli, D.: Melting and subsolidus phase relations of Fe-Si-S alloys at Mercury’s core conditions , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-13353,, 2023.